Exploring Flow Enhancements of Hydrophobic Particles in Confined Fluid Flow

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Hydrophobic particles, which are specially coated to make the surface slippery, play a crucial role in many applications in environmental engineering and energy science. For example, hydrophobic particles have been used to mitigate groundwater/wastewater contamination and improve enhanced oil recovery due to their long-term transport stability. Therefore, a better understanding of the transport and fate of such particles is an essential step towards sustainable resources for human health, well-being, and societal benefits. Despite these critical social and technological impacts, the physics of hydrophobic particles have not yet been fully explained theoretically nor reproduced in simulations and experiments due to their complex dynamics. This project is to provide a deep understanding of the key transport mechanisms enhancing the transportability of hydrophobic particles. The project will also promote extensive outreach activities, such as mobile labs, to specifically target rural areas and bridge the urban-rural divide in education.The goal of this project is to elucidate the dynamics and rheology of hydrophobic particles in a confined suspension via computational modeling and simulations along with microfluidic experimental validation. High-fidelity simulations based on the Stokesian dynamics approach will be applied to study the effects of various hydrophobicity, such as coating properties, on particle dynamics in a suspension. The central hypothesis is that the presence of hydrophobicity on the particle surface will enhance its transportability due to an enhanced particle migration toward the center of the geometry, especially at high concentrations under confinement. In pursuit of this goal, the specific objectives are: 1) establish a mathematical model for hydrophobic particles in which slip velocity can vary depending on local concentrations and flow strengths; 2) establish a computational framework to efficiently simulate a suspension of hydrophobic particles under confinement; 3) elucidate the dynamics and rheology of the sheared suspension; and 4) validate the computational results using microfluidic experiments to improve the model and underlying assumptions. The discovery that particle migration can be enhanced at high concentrations naturally suggests the existence of non-trivial rheological behaviors. In this regard, one broad theme related to examining concentrated suspensions is shear-thickening. Thus, this project is expected to provide a new understanding of shear-thickening that could be tuned by surface hydrophobicity. This new knowledge has far-reaching implications in a broad spectrum of applications because shear-thickening is widely adopted in defense and environmental systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.